This invention relates to a high time resolution electron microscope unit which applies a high-energy light beam or particle beam to the surface of a substance in a vacuum container to detect at ultra high speed the two-dimensional conditions or structural variations of the surface of the substance.
Heretofore, electron emission type electron microscopes or Muller type electron microscopes have been employed to examine the conditions of the surface of substances held in a vacuum container.
The electron emission type electron microscope operates on the following principles. When light is applied to the surface of a substance held in a vacuum container, or when the substance itself is heated, the substance emits electrons, and an electron image corresponding to the structure of the surface of the substance is formed near the substance. This electron image may be formed in enlarged scale on an output phosphor screen by means of an electron lens.
In the Muller type electron microscope, a high voltage is applied between a small needle in the vacuum and a phosphor screen confronting the small needle, thereby to form a high intensity electric field at the end of the needle. In this operation, the emission of electrons in the electric field is perpendicular to the extremely small semi-spherical surface of the needle end, and therefore the electron beam spreads radially to strike the output phosphor screen, thus forming an optical image.
The optical image thus formed corresponds to the structure of the surface of the needle. Therefore, the molecular image of a gas adsorbed onto the surface of the needle can be obtained by this method.
In the case where the variation with time of the surface of a substance under observation is slow, the above-described electron microscope can be used to visually observe this variation. However, when the surface of the substance varies at high speed, the human eye cannot follow the variation. Furthermore, even if, in this case, it is intended to take the picture of the optical image on the phosphor screen with a high-speed camera, the phosphor screen itself cannot respond to the rapid variation. For instance, in the case where the variation is of several microseconds (.mu.s), the images overlap.
It is known in the art that when a high-luminance extremely short laser pulse, electron beam pulse or ion beam pulse is applied to a substance, the energy causes a high-speed reaction to the substance in an extremely short time. As a result, the structure of the surface of the substance is changed at extremely high speed.
This reaction occurs at an extremely high rate. Therefore, in most cases only the structure of the surface which has not yet been subjected to the reaction or the structure of the surface which already has been subjected to the reaction can be detected. However, it is essential for the study of the physical properties of the substance to be able to detect the transition between these two structures.